AMORPHOUS SI AS AN INTERFACIAL CONTROL LAYER FOR SINX/INP

The use of an ultrathin amorphous silicon layer at the interface between silicon nitride and InP has been studied. The objective was to reduce the interface state density of the dielectric-semiconductor structure. Amorphous silicon and silicon nitride were deposited sequentially in the same remote plasma chemical vapor deposition chamber with a base pressure in ultrahigh vacuum. Less than 2 nm of amorphous silicon was deposited on InP by decomposing silane in a remote plasma. Three different plasmas, argon, helium, and hydrogen were tried. Silicon nitride was deposited by reacting silane with atomic nitrogen from a remote nitrogen plasma. Most of the processing steps were monitored by x-ray photoelectron spectroscopy (XPS) with sample transfer in ultrahigh vacuum. The degree of Fermi level pinning of InP at the resultant interface was studied by surface charge spectroscopy (SCS). It was found that the deposition of amorphous silicon in the nanometer thickness range could be readily controlled. The amount of native oxide on InP under the amorphous silicon layer was below the detection limit of XPS. Moreover, a 1 nm amorphous silicon layer was thick enough to protect the underlying InP from oxidation even with an exposure to ultraviolet/ozone for 15 min. SCS analysis also showed that the deposition of amorphous silicon significantly reduced the degree of Fermi level pinning of InP.